Synchrotron X-ray exploration of the growth and structure of 2D dichalcogenides

Start Date
13-12-2019 10:00
End Date
13-12-2019 11:00
Room 337, Central Building
Speaker's name
Roberto SANT
Speaker's institute
CNRS and ESRF Grenoble, France
Contact name
Claudine Romero
Host name
Nick Brookes
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Two-dimensional transition metal dichalcogenides (TMDCs) are promising materials for a variety of applications, especially in optoelectronics. However, the lack of understanding of their epitaxy, i.e. growth mechanism, microscopic structure, nature of the 2D layer-substrate interaction, etc, is still a crucial issue to address. In my work I explored a series of epitaxial growths of monolayer and thin film TMDCs grown by molecular beam epitaxy (MBE) on a variety of substrates. I studied their atomic structures and attempted the modifications of some of their properties with various in situ methods. Several systems and processes have been investigated: (i) transition metal ditellurides grown on InAs(111) substrate, (ii) the intercalation of alkali metal species between single layer MoS2 and its Au(111) substrate, (iii) the growth and the thermal treatments in H2S atmosphere of monolayer PtSe2 on Pt(111). This work relies on both phenomenological and quantitative methods based on surface X-ray diffraction, often complemented by parallel analysis performed with other probes, e.g. STM, XPS, ARPES. Most notably, I found that: (i) a charge density wave phase can be stabilized at room temperature in TiTe2 owing to the epitaxial strain in the materials; (ii) the intercalation of Cs atoms under MoS2 induces structural and electronic decoupling of the 2D MoS2 layer from its Au(111) substrate; (iii) the sulfurization of PtSe2 promotes the Se-by-S substitution in one (or both) of its two chalcogen layers, leading either to the full conversion of the selenide into a sulfide or even to an ordered Janus alloy.

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